Clarifier with influent well scum removal

ABSTRACT

A clarifier in a sewage treatment process includes efficient scum removal within the influent well, with discharge of the scum and other floatables as a dedicated waste stream separate from return activated sludge and biological scum collected in the clarifier. In one embodiment the scum removal system has an inclined scum ramp at the leading edge of each of two scum removal troughs, with a forward edge below the liquid surface. The scum troughs pass through an arc of rotation, building up scum, which accumulates and is pushed forward by the scum ramp. At least once per revolution, the moving scum ramp approaches a stationary scum surface blade that extends partially under the liquid surface and provides a barrier to the forwardly pushed scum. This blade contacts and slides up the ramp, sweeping the scum up the ramp and into the scum trough. The described arrangement greatly reduces the amount of free water with the collected effluent scum as compared to the typical designs and permits scum and gross floatables from the influent well to be trapped and contained and discharged and treated separately.

BACKGROUND OF THE INVENTION

[0001] This invention concerns sewage treatment processes, and inparticular relates to scum removal in a clarifier.

[0002] In a typical conventional activated sludge sewage treatmentprocess, a considerable volume of scum and other gross floatables enterswith the influent feed into the clarifier basin. This is distinct fromthe biological scum which arises from biological processes occurring inthe basin. In conventional clarifiers the influent scum and otherfloatables were often moved out of the influent well to be collectedalong with biological scum, over the entire clarifier surface or at theperiphery of the clarifier. The two types of scum typically werecommingled and discharged together, and where influent well scum andfloatables were collected they were delivered to the periphery of theclarifier and commingled with biological scum.

[0003] Examples are the SS Clarifiers of Enviroquip, Inc., being of opentrough design and having scum ports that move with the rake armscollecting scum and other floatables over the entire clarifier surface,with commingling. Although such systems function well to remove scumfrom the clarifier, a problem is the volume of water taken in with thescum—sometimes 200 to 300 gallons per minute, producing a very watery,diluted scum which would hydraulically overload the digester or sludgeconcentration area in the wastewater handling area.

[0004] Some prior clarifier systems have had influent wells thatprevented egress of scum or gross floatables at the surface. Some haveincluded a fixed scum beach or box within the influent well, with arotating scraper blade in the well for collecting surface scum andfloatables onto the beach or box. Some clarifiers have incorporatedrotating open scum troughs extending from center pier to the peripheryof the clarifier with ports both inside and outside the influent well.However, even where the scum and floatables were sequestered andcollected within the influent well, they were not handled separatelyfrom other biological scum for separate discharge and they were notdischarged through the center pier.

[0005] The following U.S. patents were concerned with sewage treatmentand clarifiers and have some relevance to the subject matter of thisinvention: U.S. Pat. Nos. 1,892,688, 2,295,982, 2,262,412, 2,506,927,2,661,094, 2,681,151, 2,798,041, 2,801,007, 2,822,928, 2,875,697,3,132,733, 3,166,502, 3,206,036, 3,216,570, 3,234,880, 3,314,547,3,327,867, 3,770,131, 3,892,666, 3,926,805, 3,396,102, 3,487,017,3,526,591, 4,193,877, and 5,219,470.

[0006] The prior art did not contemplate the efficient scum removalsystem of the present invention, in which virtually all scum and otherfloatables entering the clarifier's influent well are sequestered in theinfluent well, efficiently collected there in a nearly dry state, thendischarged down the center pier and separately from other scum or sludgein the clarifier, for separate subsequent processing.

SUMMARY OF THE INVENTION

[0007] In the clarifier system of the invention all access areas at thesurface of the influent well are blocked off, and the well is used as abasin and scum containment area. This allows about 90% to 95% of scum tobe captured where it enters the clarifier.

[0008] Principal innovation of this clarifier system is to expand thefunction of the influent well to include capturing virtually allinorganic gross floatables and scum inside the influent well, byproviding an additional scum collection device within the influent well,and the collection device thus feeding an isolated waste stream which ispiped down the center pier for optimal disposal of this waste streamseparate from the biological scum collected from the clarifier surfaceoutside the influent well.

[0009] Instead of removing scum using a series of scum ports at theleading edge of a sludge removal trough or scum trough as in some priorclarifiers, a preferred embodiment of the clarifier of the invention haswithin the influent well an inclined scum ramp at the leading edge ofeach rotating scum removal trough, behind which is the scum collectiontrough. The clarifier rake arms pass through an arc of rotation,preferably 360°, building up scum and other floatables as the ramps skimthe surface. The scum and other floatables accumulate on the surface andat the beach formed by the ramp and are pushed forward by the approachramp. Once per revolution each moving scum ramp approaches a stationaryscum surface blade which is secured to fixed structure above theinfluent well but which can pivot up when engaged against the ramp.

[0010] The scum blade, extending partially under the liquid surface,provides a barrier to the forwardly pushed scum and contacts and slidesup the moving ramp, sweeping the scum up the ramp and into the scumcollection trough.

[0011] This influent well scum collection device is essentially oppositeto the rotating blade/fixed scum beach that has been employed in someprior clarifier influent wells. Moreover, even those devices failed toprovide for a separate waste stream of the well-collected scum and didnot discharge down the center pier.

[0012] By reducing the volume of liquid in the scum collection system,the described arrangement greatly reduces the amount of free water withthe scum as compared to typical scum port designs. The new systempermits the scum in the influent well, including other floatables, to betrapped and contained with little liquid, prior to being disposed of andtreated separately from biological scum captured elsewhere in theclarifier basin, and without commingling with sludge or returning to thehead of plant.

[0013] Although the well scum is efficiently collected using thedescribed scum ramp sweeping the influent well, other systems operablewithin the influent well, such as ports or slide gates, couldalternatively be used. One alternative sometimes preferable is an opentrough with scum ports which terminates at the influent well, used inthe same clarifier system with a traditional scum box mounted at theperiphery of the clarifier to capture biological scum to be handledseparately. The open scum trough within the influent well conducts thecollected scum and inorganic floatables into a waste stream which exitsthe center pier separately.

[0014] The system of the invention thus provides for a cleaner watersurface outside the clarifier's influent well, cleaner effluent from theclarifier, and segregation of gross floatables and scum from biologicalscum, thereby allowing optimal disposal or use of each waste stream. Inaddition, the system contains influent well scum even when the scumpumps are idle and provides for very little dilution of gross floatablesand scum captured in the influent well.

[0015] It is thus among the objects of the invention to make moreefficient the operation of a clarifier and other systems in an activatedsludge sewage treatment process, by collecting most of the scum of theclarifier system as scum enters the influent well with the influentfeed, and by discharging this scum and other floatables in a dedicatedstream down through the center pier with very little volume of water.These and other objects, advantages and features of the invention willbe apparent from the following description of a preferred embodiment,considered along with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a plan view schematically illustrating a central portionof a clarifier basin including an influent well, rotatable drive cageand the scum collecting innovation of the invention.

[0017]FIG. 1A is a view similar to FIG. 1, but showing a variation inlocation of certain scum collection components.

[0018]FIG. 2 is a schematic elevation view partially in section and asseen along the line 2-2 in FIG. 1, showing equipment in the centralportion of the clarifier, including the drive cage frame, influent andexit ports and conduits for activated sludge and scum, and the scumremoval apparatus of the invention.

[0019]FIG. 3 is a plan view similar to FIG. 1, showing another form ofscum collection in the influent well.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0020] In the drawings, the plan view of FIG. 1 shows a central area 10of a clarifier basin, the basin itself being much larger than what isseen in the drawing, as in conventional clarifier basins having acentral influent well.

[0021] The clarifier's central area 10, as seen in both FIGS. 1 and 2,includes an influent center pier column 12 which is stationary andsolidly secured to fixed structure at the base of the clarifier basin,such as concrete, and as in other conventional clarifiers, it suppliessupport for equipment which sweeps around the preferably circular basinto aid in the clarifying function. The pier column 12 may have a topannular flange 13. FIG. 1 shows a pair of return activated sludgetroughs 14, extending in opposite directions generally radially awayfrom the center pier column 12, each sludge trough forming a part of arake arm which rotates around the clarifier basin about a center ofrotation 16. The return activated sludge troughs 14 are connected to andsupported at least in part by a return activated sludge (RAS) collectionbox 18 which is secured to a drive cage frame 20, portions of which areseen in FIG. 2. The drive cage frame 20 is driven in a slow rotationabout the center pier column 12, by equipment of a type which is wellknown and commonly used in conventional clarifiers, including a rotatingdevice (not shown) mounted on top of the center pier column 12.

[0022]FIG. 2 shows the RAS collection box 18 with interior equipmentshown in dashed lines. The influent pier column 12 continues up throughthe PAS collection box, and where the column 12 penetrates the bottom 22of the RAS collection box, a seal is provided between the pier and thecentral hole in that bottom panel 22. Such seals are well known inclarifier equipment.

[0023] As seen in FIG. 2, within the interior space of the RAScollection box are RAS return ports 24 on the center pier column, forallowing sludge collected in the collection box to pass by gravity intothe center pier column, to be discharged down a drain hole 25 (dashedlines FIG. 1) and through an RAS removal pipe 26 which may be at or nearthe center of the pier column as shown. At the same time, influentsludge is fed up through the influent center pier column 12, in thespace surrounding the RAS removal pipe 26, to be initially dischargedinto the clarifier through influent feed ports 28. That portion of theinfluent center pier column has a ceiling 30 surrounding the top of theRAS removal pipe 26, also serving as a floor for the chamber above, withthe RAS drain hole 25 being in that floor.

[0024] Above the RAS return ports 24 is a scum collection box 32 thatrotates with the RAS collection box, having a floor at 34, separatingthis scum collection area from the RAS collection box 18 below. A floor34 a in the stationary center pier column appears at about the samelevel as the scum box floor 34, although it could be lower. The outerfloor 34 rotates, being engaged with the exterior of the center piercolumn in a rotary seal (not specifically shown).

[0025] The scum collection box 32 receives scum from scum collectiontroughs 38 which extend from the scum collection box 32 generallyradially and only within the confines of an influent well 40 defined byan influent flocculation skirt 42 (seen in FIG. 1). The skirt 42 iscircular or essentially circular in shape and rotatable with the RAScollection box 18, scum collection box 32 and rake arms, of which theRAS troughs 14 form a part. The influent flocculation skirt 42 is notshown in FIG. 2, but FIG. 1 shows that it extends an essentially fullcircle to. define the influent well 40, broken only by the RAS troughs14 that extend substantially to the far reaches of the clarifier basin.As is typical of an influent flocculation skirt in a clarifier, theskirt 42 extends from above the surface of the water and sludge (surfaceshown at 44 in FIG. 2) down to several feet above the bottom of theclarifier basin. The influent well typically is about four to eight feetin depth.

[0026] Scum collected in the scum collection troughs 38, shown in FIG. 2as secured to the return sludge collection troughs 14, flows inwardlytoward the center pier column and into the scum collection box 32, whereit is collected on the floor 34 of the scum collection box, radiallyoutwardly of the center pier column as can be seen particularly fromFIG. 1. By its own accumulation and gravity, the scum then pours throughscum return ports 46 into the interior of the center pier column, to aninternal scum accumulation area. From both FIGS. 1 and 2 it can be seenthat the scum then flows out of this storage area on the internal floor34 a of the center pier column via a drain 48 and connected scum removalpipe 51 that ultimately takes the scum effluent to the exterior of thecenter pier column, for separate treatment. Such separate collection anddischarge, without commingling with either biological scum collectedelsewhere in the clarifier or sludge, is an important feature of theinvention.

[0027] As explained above, the clarifier apparatus of the inventioncollects scum and other gross floatables which initially enter theclarifier through the influent feed ports 28 in the center pier column,and contains them within the influent well 40. This is in contrast withmany other systems which deliver the scum along with the influent feedthroughout the volume of the clarifier basin, or which collect well scumand biological scum in a common scum trough. A very large percentage oftotal scum which appears within the clarifier is present in the influentfeed, and since the scum and other floatables will float to the surface,they can be contained within the influent well, by the influent skirt42. Some prior systems have contained the scum in an influent well, andeven collected the scum and floatables there, but then have piped thescum and floatables to other areas of the clarifier to be commingledwith biological scum.

[0028] As the rake arms, RAS troughs 14, scum troughs 38 and influentskirt 42 rotate with the RAS collection box 18 about the center piercolumn 12, a scum ramp 50 of this preferred embodiment, associated witheach rake arm and preferably connected to each scum collection trough 38(FIG. 2), sweeps forward in an arc through the influent well. Each scumcollection ramp 50 forms a beach, being angled and with a lower lip 52below the liquid surface and an upper edge 54 above the liquid surface.FIG. 2 shows this clearly, with the liquid surface 44 approximatelymidway up the ramp in the illustrated embodiment. This can vary, theimportant consideration being that the lower lip 52 of the scum ramp bebelow the surface sufficiently to gather all floating debris, includingscum. The liquid surface 44 should not be so high up the ramp as to pourliquid into the scum collection troughs 38.

[0029] As the scum ramps 50 sweep through the influent well 40, theyaccumulate scum and other floatables against the ramp, these floatablescontinuing to be pushed forward in an arcuate path by each ramp. Theramps thereby gather virtually all floating scum and debris,accumulating them in front of the ramp. To collect this floatingmaterial into the scum collection troughs 38, a scum surface blade 56 isprovided. The blade 56, necessarily supported from above so as to allowpassage of the rake arms, RAS troughs 14 and the scum collection troughsthemselves, is secured to fixed structure such as the access beam bridge58 of the clarifier, illustrated in part in FIG. 2 for this preferredembodiment.

[0030] As FIG. 2 shows, a fixed structural frame member 60 can extenddown from a part of the access beam bridge, to a pivot connection 62.From there, the scum surface blade 56 is supported on one or more pivotarms 64, in a manner that fixes a lower limit, normal position of theblade but allows it to swing upwardly about the pivot 62 when forcedupwardly. This occurs when the scum surface blade 56 encounters theinclined scum ramp 50. At that point the blade 56 has trapped theadvancing accumulated scum and debris, causing it to build up moredensely against the scum ramp and to gather together somewhat. When thescum surface blade 56 encounters the ramp, the ramp cams the scum bladeto pivot upwardly and ride up the ramp, thus sweeping the accumulatedand gathered debris up and over the ramp into the scum collection trough38. In a preferred form of the invention, this occurs once perrevolution, there being one scum surface blade within the influent well.The blade may be formed of an elastomeric, rubbery material so that itpasses over the scum trough 38 and the RAS trough 14 without difficulty.

[0031] By this efficient scum removal system an effluent ofscum/floatables is produced with very little free water.

[0032] In another embodiment of the invention, scum and gross 10.floatables are again collected within the influent well, and aredischarged separately from sludge and biological scum collectedelsewhere in the clarifier, but the scum collection device within theinfluent well is different. FIG. 3, somewhat similar to FIG. 1, shows analternative arrangement which does not include the scum ramp or beach 50and the scum surface blade 56 illustrated in FIGS. 1 and 2. In thisembodiment, a scum collection device comprises an open scum collectiontrough 70 with scum ports 72. The scum trough 70 extends only within theinfluent well 40, bounded by the influent flocculation skirt 42, andpreferably is secured to the return activated sludge trough 14 as in theprevious embodiment, at the leading side of the sludge trough 14 as therake arms and troughs 14 rotate. One such open scum collection trough 70is included on each side of the center pier in a preferred embodiment.The open scum collection troughs 70 have inner ends 76 which open intoand deliver scum into a scum collection box 32 as in the previousembodiment. Accumulation of the scum within the box 32, and discharge ofthe scum and floatables through the center pier column, preferably isthe same as in the previously described embodiment, including a scumremoval pipe 51. The difference is that the open scum troughs 70 take ina considerable volume of water along with the scum and gross floatables,thus producing a more diluted discharge. However, the dischargenonetheless forms a separate stream from collected sludge and frombiological scum collected in other regions of the clarifier outside theinfluent well. Such separate collection and discharge is an importantfeature of the invention.

[0033]FIG. 1A shows a variation to what is shown in FIGS. 1, 2 and 3, inthe location of the scum collection troughs 38 and the attached scumramps or beaches 50. This variation should be considered as applyingequally to the embodiment shown in FIG. 3, wherein such ramps are notincluded.

[0034]FIG. 1A illustrates that the scum collection troughs 38 need. notbe adjacent to and essentially parallel to each rake arm 14 as shown inFIGS. 1, 2 and 3. Rather than being secured to the rake arms, the scumcollection troughs 38 can extend in a different direction from the rakearms, still extending generally radially outwardly from the drive cage,as shown. Other directions are possible, as desired, since the scumcollection troughs 38 need not be angularly equidistant from the tworake arms 14.

[0035] The influent well 40 of the clarifier system of the invention hasan additional benefit over prior clarifiers. Since the influentflocculation skirt 42 is essentially fully closed, from above thesurface of the liquid to below the liquid surface, it will contain foamwhich builds up within the influent well. This is contrasted with priorinfluent wells which permitted scum to flow outwardly throughout thesurface of the clarifier. The added benefit here is that the scum isessentially fully contained within a small area in the center of theclarifier basin, and can much more easily be treated and controlled fromthis inner region. Some foam is caused by certain bacteria, and otherfoam is caused by other sources. With the arrangement of the invention,the foam can be treated, either with bacteria-killing agents or withother anti-foaming agents, solely from within the influent well area.Thus, efficient and effective scum control in the clarifier basin isachieved according to the invention by (a) providing a skirt whichcloses off the outward movement of scum, the great majority of whichoccurs within the influent well, and (b) treating scum solely within theinfluent well, thus eliminating any need to apply foam control agents oranti-bacteria agents for purpose of controlling foam within the largeremaining area of the clarifier, outside the influent well.

[0036] The above described preferred embodiments are intended toillustrate the principles of the invention, but not to limit its scope.Other embodiments and variations to this preferred embodiment will beapparent to those skilled in the art and may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

I claim:
 1. In a clarifier which forms part of a sewage treatmentsystem, the clarifier having a clarifier basin, an influent center piercolumn in the basin, a drive cage which is rotatable and which generallysurrounds the influent center pier column, and one or more elongatedrake arms which extend radially outwardly from and rotate with the drivecage, extending generally to an outer wall of the clarifier basin, andthe clarifier also including an influent flocculation skirt surroundingthe influent center pier column and drive cage and extending above andbelow the liquid surface in the clarifier basin and defining an influentwell around the drive cage and influent center pier column, a scumcollection system within the influent well, comprising: an elongatedscum collection trough connected to and driven rotationally with thedrive cage, extending generally radially outwardly from the drive cagewithin the influent well, surface scum collection means within theinfluent well for gathering floating surface scum and other floatableswithin the influent well and delivering the scum and other floatablesinto the scum collection trough, and scum discharge means connected tothe influent center pier column for receiving the scum and otherfloatables from the scum collection trough and delivering the scum andfloatables to a position exterior of the center pier column, separatefrom other waste streams out of the clarifier, for separate treatment ordisposal.
 2. The apparatus of claim 1, wherein the scum collectiontrough extends substantially out to the influent flocculation skirt. 3.The apparatus of claim 1, further including a scum collection boxconnected to the scum collection trough and surrounding the influentcenter pier column, the scum collection box being positioned to receivescum and other floatables collected in the scum collection trough, andhaving sealing means between a floor of the movable scum collection boxand an exterior surface of the fixed center pier column, and the centerpier column including scum return ports positioned to receive inflowingscum and floatables from the scum collection box, with an internal floorin the center pier column to define an interior scum accumulation area,and further including a drain in the internal floor of the center piercolumn, with a scum removal pipe connected to the drain and arranged todeliver the collected scum and floatables as a scum effluent stream tothe exterior of the center pier column, for separate disposal ortreatment of the effluent scum and floatables.
 4. The apparatus of claim1, wherein each scum collection trough includes scum ports at leadingedges positioned to take surface scum and gross floatables into the scumcollection trough as the trough sweeps around the influent well.
 5. Theapparatus of claim 1, wherein the surface scum collection means furtherincludes a scum accumulation ramp secured on a forward side of each scumcollection trough, the ramp having a forward edge positioned to bebeneath the surface of the liquid in the influent well and a rear edgeabove the surface and adjacent to a forward edge of the scum collectiontrough, and a scum surface blade supported on fixed, non-rotationalstructure of the clarifier and not rotatable with the rake arms, withmeans establishing a normal position of the blade while allowing upwardmovement when upward force is applied, the scum surface blade beingsuspended from above and extending down into the liquid within theinfluent well of the clarifier, in the path of the scum accumulationramps, and so positioned that accumulated scum within the influent wellis pushed forward around the well by each of the scum ramps, and when ascum ramp approaches the scum surface blade, the blade prevents furtheradvance of the accumulated scum, causes the scum to build up moredensely against the scum accumulation ramp, then contacts the ramp andslides up the ramp, thereby sweeping the scum up the ramp and over theramp into the scum collection trough.
 6. The apparatus of claim 5,wherein the scum surface blade comprises a generally planar, rectangularpiece of flexible, elastomeric material.
 7. The apparatus of claim 6,wherein the means establishing a normal position of the scum surfaceblade includes a pivot arm securing the scum surface blade to said fixedstructure of the clarifier so as to allow the arm to pivot about agenerally horizontal axis, thereby allowing the scum surface blade toswing up when sliding on the scum accumulation ramp.
 8. A method forcontrolling foam caused by bacteria or other sources in a clarifierbasin of a sewage treatment system, comprising: providing an influentwell in a central region of the clarifier basin, the influent well beingdefined by an influent flocculation skirt surrounding an influent centerpier column and drive cage, the skirt extending above and below theliquid surface in the clarifier basin so as to provide a closed barrierwhich essentially contains any foam which builds up on the surface ofthe liquid within the influent well, and during operation of theclarifier basin, spraying the foam contained within the influent well,with either a bacteria-killing agent or an anti-foaming agent in orderto control the foam, whereby foam in the clarifier basin is controlledfrom the relatively small area of the influent well, eliminating theneed to actively control foam outside the influent well.